ML20058K663
| ML20058K663 | |
| Person / Time | |
|---|---|
| Site: | Monticello  |
| Issue date: | 08/03/1978 |
| From: | Wachter L NORTHERN STATES POWER CO. |
| To: | James Keppler NRC OFFICE OF INSPECTION & ENFORCEMENT (IE REGION III) |
| References | |
| IEB-78-11, NUDOCS 9102130426 | |
| Download: ML20058K663 (4) | |
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t NORTHERN 5TATES POWER COMPANY 4 wuca#ous. uswnescu es4oi 1
Aaguet 3, 1978 Mr. James G. Keppler Director - Region III Off12e of Inspection and Enforcement L'nited States Nuclear Regulatory Commission 799 Roosevelt Road Glen Ellyn, Illinois 60137
Dear Mr. Keppler:
MONTICELLO NUCLEAR GENERATING PLANT Docket No. 50-263 License No. DPR-22 The following is our response to IE Bulletin No. 78-11 (dated July 24, 1978) for the NSP Monticello Nuclear Generating Plant:
Item A-1 A.
Welding Procedure Qualifications Standard butt veld and water-backed butt veld tests were made to comply with the requirements of ASME Section III, Subsection NE, and ASME Section IX for veld procedure qualification. The veld =ents were tested for tensile, bend, and Ocpact properties.
In addition, various special water-backed weldments were qualified to further establish detailed field welding parameters and techniques.
Good results were obtained from bend, impact, and eferohardness tests l
of overlay welds which simulated those that have been applied directly onto the torus.
r B.
Velding Procedure All strengthening of the torus supports were done using normal velding methods on top of special, previously-applied weld overlays.
In addition, the edges of all overlays (i.e., the " toe" of the welds) had te=per beads applied on the first layer of weld metal to within 1/8" of the torus shell, so to te=per the heat-af fected zones on the shell plate.
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NOF 4ERN GTATED POWER Ct IPANY Mr. James C. Keppler August 3,1978 Page 2 The Monticello torus support modification required two widths of overlay -- approximately 3-inch veld overlays where side-stiffener plates were to be attached and only 1-inch veld overlays in the other areas where the web and wing plates were to be strengthened by simply building up the existing fillet velds. This required l
two different overlay techniques --
- I 1.
All 3-inch wide overlays were made in the vertical-up l
position by first applying, at about 3 inches from the existing fillet veld, edge beads and temper beads with 1/8" electrodes. Then, the remaining overlay between i
these edges and the existing fillets were completed by using 5/32" electrodes and weaving the beads approximately l
2" vid e.
j 2.
The 1-inch wide overlays were made in both horizontal and vertical-up positions by applying one layer using 3/32" l
electrodes, followed by temper beads, and a second laver using 1/8" electrodes.
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A separate procedure was used to repair any defects on the torus shell; such as, undercut, are strikes, or improper temper bead spacing (from the edges of the first layers). The technique was very similar to that specified for the 1" wide overlays.
In addition, asbestos was taped on the torus shell adjacent to the weld areas as a precaution i
to minimize are strikes.
l All overlay areas were controlled so that, once started, each overlay
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was required to be completed as soon as possible and, in all cases, at least during the same workday shift. Welding of side stiffener plates l
vas sequenced to minimize restraint stresses on the torus overlays.
C.
Welder Qualification i
All welders were qualified per ASME Section IX by velding grooved-plate butt velds with backing strips. In addition, special lectures j
and practical training were given each velder regarding.the overlay
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and te=per bead techniques and precautions. Each welder was then required to pass both a written exam and practical welding test on l
overlays and temper beads. The practical test was monitored by a j
Q.C. Inspector in the same manner as for future welds (i.e., visual exa=ination, travel speed, current, etc).
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t NORTHERN STATES POWER COMPANY Mr. James G. Keppler I
August 3, 1978 i
Page 3 D.
Electrode Control All electrodes were the " Atom Are" brand of Chemtron Corporation, l
Class E7018, and were purchased in hermetically-sealed cans. All electrodes met the requirements of ASME Section 111, Article NE-2000.
l Af ter opening, all electrodes were baked for 1 to 11/2 hours at I
8000F and then were transferred to controlled holding ovens. At th?
start of each shif t, each welder was given about enough electrodes for the planned day's work; and, at the end of shift, any re=aining electrodes were discarded. Electrodes were kept in portable heated
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ovens at the work stations during each shif t.
t Item A-2 (Condensation)
Condensation was not considered a problem since welding was performed i
- during the very dry, low hu=idity Minnesota winter, and the temperature j
of the torus shell was at.approximately 800F. However, it was specified j
that all surfaces to be velded shall have been cleaned i=nediately before welding (i.e., within 30 minutes) with Spotcheck Cleaner Type SKC-NF, For=ula B (made by Magnaflux Corporation). Such cleaning was verified l
on the veld data sheets.
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Item A-3 (NDE Examinations) i All welds were examined by the dry magnetic particle yoke method. No j
relevant indications were reported by this =ethod.
i Since the project records consist of over 8500 pages, only eight veld
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sequences were checked. All eight velds were found to have been j
magnetically examined af ter waiting a period of at least one week from j
the time of welding. No such time period had, however, been specified j
for the project.
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Item B (Reexamination) l Since it would be extremely-difficult to determine the chronology of
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non-destructive examinations relative to each corresponding welding date j
from the over 8500 pages of microfilmed records, it was decided by NSP to remove the paint from all overlay weld-to-torus base metal surf aces i
and to reexamine all such areas using the dry magnetic particle yoke
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method in accordance with ASME Section III, Article NE-5000.
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f NORTHERN STATES POWER COMPANY Mr. James G. Keppler August 3, 1978 Page 4 These examinations revealed a few minor linear indications on two adjacent columns, on the lower side of the lower horizontal wing plates, along the overlay-to-torus veld edge, none exceeding 1 1/2 inch length. These indications were removed by minor amounts of grinding; i.e.,
grinding to a depth of less than 1/32" except one 1" long area was ground to a depth of about 1/16". Removal cf indications was verified by magnetic particle and liquid penetrant examinations.
Very truly yours, I
L.J.f h Y $
Wachter Vice President - Power Production i
and System Operation cc:
Mr. G. Charnoff NRC Office of Inspection and Enforcement Washington, D.C.
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